THIS IS A RUSH TRANSCRIPT. THIS COPY MAY NOT BE IN ITS FINAL FORM AND MAY BE UPDATED.

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WOLF BLITZER, CNN ANCHOR: Happening now, breaking news: closing the deal. Donald Trump now assured of the Republican presidential nomination after a handful of delegates throw their support behind him, giving him the 1,237 needed to be the GOP nominee. We are standing by for a Trump campaign rally this hour.

Misquoted. Trump walks back statements by his campaign chairman about his potential pick for vice president and his controversial ban on Muslims entering the United States. Is Trump taking a new position?

Terrorist smuggling. ISIS fighters now hiding among groups of migrants trying to get into Europe, the terrorists said to be taking extreme measures to blend in. How many have made it and what are they plotting?

And new White House. A new one. President Obama signs a lease on a Washington mansion in an exclusive neighborhood that he will call his home after he leaves the Oval Office, but post-presidential security presents a major challenge. How will the Secret Service keep the first family safe? How much will it cost taxpayers?

We want to welcome our viewers in the United States and around the world. I'm Wolf Blitzer. You're in THE SITUATION ROOM.

ANNOUNCER: This is CNN breaking news.

BLITZER: We are following the breaking news, Donald Trump tightening his grip on the Republican presidential nomination with a handful of uncommitted delegates now throwing in their support.

The billionaire businessman has the 1,238 delegates, he has 1,238 -- that's one more than the number needed to become the GOP standard- bearer when the party convenes in July. Trump is holding a rally in Montana this hour. We are standing by to hear from the presumptive Republican presidential nominee.

We are also following security concerns surrounding the next home of President Obama and his family. They have leased a nine-bedroom mansion in an exclusive Washington neighborhood where they plan to live when the president and his family, they leave the White House less than nine months from now.

But tonight, we're learning that protecting the president and his family will be costly, will be challenging. We're covering all of that, much more this hour with our guests, including Congressman Lou Barletta. He's a Donald Trump supporter, a member of the House Homeland Security Committee.

And our correspondents and expert analysts, they are also standing by.

Phil, we are standing by to hear from the presumptive Republican presidential nominee. What's the latest?

PHIL MATTINGLY, CNN CORRESPONDENT: Well, Wolf, he is now expected out here in a matter of moments. And obviously this is a huge day for his campaign, clinching the nomination, surpassing 1,237 delegates.

The people here were just informed of that fact by one of the opening speakers. It was met with large applause. But Trump today talking to reporters, not spending a lot of time basking in that moment, instead focusing on his next target, swinging back at not just the likely Democratic nominee, Hillary Clinton, but also President Barack Obama.

MATTINGLY: Trump speaking just hours after the sitting president, overseas in Japan, said this about how foreign leaders perceive the New York billionaire.

BARACK OBAMA, PRESIDENT OF THE UNITED STATES: I think it's fair to say that they are surprised by the Republican nominee. They are not sure how seriously to take some of his pronouncements, but they are rattled by it.

MATTINGLY: Trump taking the critique in stride and saying it's actually beneficial in the wake of the current administration's actions.

TRUMP: If they are rattled in a friendly way, that's a good thing. He's a president who has done a horrible job. Everybody understands that. He's a president who has allowed many of these countries to totally take advantage of him.

MATTINGLY: Trump back on the trail in North Dakota after bypassing the key number of 1,237 delegates needed to clinch the nomination.

TRUMP: The folks behind me got us right over the top.

MATTINGLY: Pivoting quickly to his likely next opponent, Hillary Clinton.

TRUMP: Here I am watching Hillary fight, and she can't close the deal. And that should be such an easy deal to close.

MATTINGLY: And continuing what has become a round-by-round slugfest between the presumptive nominee and Democratic Senator Elizabeth Warren.

TRUMP: She's a woman that has been very ineffective, other than she has got a big mouth.

MATTINGLY: Trump's attacks on Clinton a message the Republican Party hopes will resonate, even as it continues the process of coming together behind its oft-controversial standard-bearer.

REP. PAUL RYAN (R-WI), SPEAKER OF THE HOUSE: What I'm most concerned about is making sure that we actually have real party unity, not pretend party unity, real party unity, because we need to win this election in the fall.

MATTINGLY: Unity inside Trump's campaign, not unlike with the party, a work in progress, Trump's comments coming the day after the removal of his national political director amid continued tensions at the top of his campaign, all as Trump's campaign adviser appeared to reject the possibility of a woman or a minority as Trump's running mate, saying it would be -- quote -- "viewed as pandering."

[18:05:20]

Trump walking that back today.

TRUMP: He's been misquoted actually a lot, but we're going to have women involved at the absolute highest levels.

MATTINGLY: And, even under constant attack, remaining steadfast on his refusal to release his tax returns until the completion of an IRS audit.

TRUMP: I don't know of very many people that have been audited for 15 years. I'm audited all the time. So, I don't know what that's all about, but the IRS has been very professional.

And, as we move along, as soon as that is finished, whenever that may be -- and hopefully it's going to be before the election. I'm fine with that that. OK?

(END VIDEOTAPE)

MATTINGLY: Now, Wolf, what's interesting to note here is, Montana was actually one of the June 7 states that all of the Republican campaigns were targeting when they still thought a contested convention was possible.

Obviously, that completely off the table now, and Donald Trump did take at least one moment to celebrate, posting this picture on Instagram celebrating on his flight from North Dakota to Montana with, of course, a McDonald's Big Mac and Diet Coke -- Wolf.

BLITZER: He's always said he likes McDonald's.

All right, thanks very much for that, Phil Mattingly.

Let's get some more on the presumptive Republican nominee.

Our senior White House correspondent, Jim Acosta, is joining us.

Jim, Trump just about to speak in Montana. Earlier, he had a news conference. You were there. What did he say about actually wanting to debate Senator Bernie Sanders?

JIM ACOSTA, CNN SENIOR WHITE HOUSE CORRESPONDENT: Yes.

Wolf, it appears to be game on after his appearance on "The Jimmy Kimmel Show" last night, where Trump seemed to be joking about the idea. The presumptive GOP nominee made it clear at this news conference here in Bismarck today he wants to debate Bernie Sanders.

And so he says this will happen as long as the event raises millions of dollars for charity and he added his campaign has been in touch with team Sanders to make this happen. Here's what he had to say about this earlier today, Wolf.

(BEGIN VIDEO CLIP)

TRUMP: It should be in a big arena somewhere, and we could have a lot of fun with it. I would love to debate Bernie actually. The problem with debating Bernie, he is going to lose, because honestly his system is rigged, just like our system is rigged.

Look, if I didn't win by massive majorities, I wouldn't be standing here talking to you today.

(END VIDEO CLIP)

ACOSTA: Now, Trump also said he would debate Elizabeth Warren when asked -- when I asked him if he was interested in a face-off with the Massachusetts senator. He may have plenty of practice before he goes up against his likely Democratic opponent, Hillary Clinton, Wolf.

But this just goes to show you how unprecedented this campaign is. Wolf, Donald Trump should be preparing to debate Hillary Clinton, not Bernie Sanders and Elizabeth Warren.

BLITZER: Yes. When I spoke a little while ago with Hillary Clinton, she said she's actually looking forward to debating Donald Trump, but that is going to have to wait until after the convention, September, October, those three regularly scheduled presidential debates.

Jim Acosta, thanks very much.

Let me ask you one more question, though, Jim, before I let you go. This was a scripted speech he later gave where you are in North Dakota. What, it's only the third time he has read a speech from a teleprompter?

ACOSTA: Right. That's right. He likes to give Hillary Clinton grief for using teleprompters. He used one here. He has more policy speeches coming in the coming weeks, we understand, Wolf. He's already delivered one on foreign policy.

And as for the speech on energy, Wolf, it is important to note Donald Trump would completely undo President Obama's climate agenda, saying today that he would do away with the Paris climate agreement, he would basically pull the United States out of that, and he would ask TransCanada to submit another application to build that Keystone pipeline that was such a drama during the second Obama term -- Wolf.

BLITZER: I remember. All of us remember that, of course. All right, Jim Acosta, thanks very much.

ACOSTA: That's right.

BLITZER: Let's get more on all of this.

Republican Congressman Lou Barletta of Pennsylvania is joining us. He's a member of the House Homeland Security Committee. He has also endorsed Donald Trump for president early on.

Congressman, thanks very much for joining us.

REP. LOUIS BARLETTA (R), PENNSYLVANIA: Good to be here, Wolf.

BLITZER: So, we heard Donald Trump say it is actually a good thing, if he were president, if he rattled world leaders. How can the U.S. have productive foreign relations if America's enemies and allies for that wonder if they're all being rattled, even in a -- quote -- "friendly way"?

BARLETTA: I think it is a good thing, Wolf, actually.

You never want anyone to know, to predict what you're going to do. And I think we saw that with this administration, drawing a red line in the sand and watching people cross it and doing nothing. I think as far as national security, it's always good to have the other side just not sure exactly what you're going to do.

BLITZER: And allies as well, as opposed to enemies or adversaries of the United States? You want our allies not to be sure what the U.S. is going to do?

BARLETTA: No, I don't think you will see that in a Donald Trump presidency.

I think what you will see totally different than we are seeing now is that our allies will know that the American -- the United States of America is going to stand behind you.

[18:10:05]

When you're a friend of the United States, we're going to stand with you. Right now, our allies don't know that. Our allies can't trust us and our enemies don't fear us. And I think this will be totally different than what we're seeing today.

BLITZER: A lot of us were surprised, Congressman, when Donald Trump went after the New Mexico governor, Susana Martinez. She's a Republican, Hispanic. She's chair of the Republican Governors Association.

What good does it do for him to do that, especially when he is trying to unify the Republican Party?

BARLETTA: Well, you know, Donald Trump has been a self-proclaimed counterpuncher. He will tell you if he feels he is getting jabbed or punched, he is going to punch or jab back.

And I think he uses these instances to really highlight something. We really want to highlight how many are on public assistance and food stamps, and not having a job, and not seeing a way out of poverty. And he has a way of bringing an issue to the forefront, and when you peel back what he says, you end up talking about the issue that he really wants to talk about.

I think he's been masterful in doing it. And he's not going to hold back. That's what people like about Donald Trump. He will say what's on his mind. And if you like it, you like it, and if you don't, you don't. He may say something great about her tomorrow if he finds something that he thinks is great. He says what's on his mind and I think people like that.

BLITZER: Because basically he was apparently upset because she didn't come to the event in New Mexico,she was busy doing some other stuff, she hadn't endorsed him, earlier, she had endorsed Marco Rubio.

And I guess the bottom line question, she's a woman, she's a Republican, she's head of the Republican Governors Association, a Latina. You need all that kind of support if you're going to be elected president if you're a Republican, right?

BARLETTA: Yes, but he's not a typical politician, right? That's again the attraction of the American people, is, he doesn't do what's politically correct, he doesn't do what political advisers would tell him to do, he does what he thinks is on his mind at the time.

And like I said, it doesn't mean that tomorrow if he finds something that he likes that she did that he wouldn't praise her as well. And people like that honesty, they like that he is not caged, and not giving talking points and things -- how to say things. He is Donald Trump, and he will say it as he sees it.

BLITZER: And that strategy clearly worked in defeating 16 or 17 Republican rivals, Republican challengers. But now that he's for all practical purposes the Republican presidential nominee, shouldn't he perhaps moderate or modify his tone a bit in order to get everybody on board?

BARLETTA: I think he has. Just I see it myself personally in Washington in the number of how he

is bringing the Republican Party together, and unifying the Republican Party and how he is on a one-to-one basis with people, and how impressed they are when they see the boardroom Donald Trump and the real Donald Trump and how he wants to hear your opinion, he values our policy ideas and he is taking it in.

And I think you're seeing a transition now into someone who will be a great president.

BLITZER: But even your leader, the speaker of the House, Paul Ryan, he still hasn't been able to endorse him, to say he's going to support him.

That's almost -- I think it's almost unprecedented for a speaker of the House to not endorse the presumptive nominee of his own party.

BARLETTA: Yes. And that's all right. Paul Ryan will come when Paul Ryan is ready.

He's a policy wonk. He wants to feel good about the agenda that he's been working on and we have been working on in the House, and they're talking every day and talking about policy and that's the other thing that I like about Donald Trump.

He has not strong-armed anybody on the Republican side to get on board. When Paul Ryan is ready, he will come on board. In the meantime, Donald Trump is going to keep on doing what he is doing.

BLITZER: I want you to stand by, Congressman.

We're also standing by to hear directly from Donald Trump. He's being introduced at a rally in Billings, Montana, right now. That's one of his aides, Stephen Miller, who is speaking over there. We will have live coverage. We will continue our conversation right after this.

(COMMERCIAL BREAK)

[18:18:35]

BLITZER: We're standing by to hear from Donald Trump at a campaign rally in Billing, Montana. You're looking at live pictures from that rally.

Trump has now topped the number of delegates need to lock down the Republican presidential nomination. Did that today.

We are back with Republican Congressman Lou Barletta of Pennsylvania. He's a member of the House Homeland Security Committee and he's a Donald Trump supporter.

Congressman, Paul Manafort, I don't know if you know him personal. He is a top aide, the campaign chairman for Trump right now. He said in an interview with Huffington Post that Trump will soften his temporary -- proposal for temporary ban on Muslims coming to the United States, but Trump avoided getting into specifics on that in his news conference earlier today when he was asked about it.

Here's the question to you. Would you support a softening of that proposed ban?

BARLETTA: Yes, I think I would, you know, and, again, I believe that has been part of his strategy in this campaign, when he had to beat 17 professional candidates on the Republican side, in saying something that really shocks people.

And then -- again, then you start talking about the issue. And then at the heart of it, you're debating whether or not it's a valid issue and how do we deal with it. And many of the issues that most politicians wouldn't want to bring up, he has been able to do that by saying something that really catches everybody's attention.

[18:20:00]

And then we end up having a debate on the issue. He is a businessman. So when you go into a negotiation, obviously, you go in bidding very high, knowing that you're willing to settle at some other point.

And I think he uses some of that strategy into getting to the place where he wants to get in, and that's to have a real debate on how we deal with that problem.

BLITZER: When I hear you're saying these are opening bargaining positions, that he is willing to modify as negotiations get under way, would it be the same thing his proposal -- he has repeatedly said he wants to deport 11 million undocumented immigrants who are living here in the United States.

Are you with him on that as well?

BARLETTA: Well, I am not going to speak for him.

Obviously, he does a great job of speaking for himself. I'm just saying that, you know, I think, in the world of business, a strategy is always there's a sweet spot where you want to get to, but to get to that point, you can't start there because you never end up there.

That's how I got to Congress, is fighting illegal immigration as the mayor of Hazleton. And here we are today. We wouldn't even be talking about this issue if it wasn't for Donald Trump. I'm in Congress now six years. Our borders are still open. We haven't done anything about illegal immigration. The American people are fed up with it. They're seeing their wages depressed.

So at the end of the day, Wolf, I believe that because of Donald Trump we will secure our borders, and that's the first step. Everybody in Washington agrees, Democrats and Republicans, let's secure the borders, but we don't do it.

So, wherever we end up, we will be better off because of how Donald Trump brings these issues out into the public.

BLITZER: Very quickly, his campaign chairman, Paul Manafort, said Trump "operates by starting the conversation at the outer edges and then brings it back toward the middle."

I guess the question to you is, do you think he will stand by his pledges so far on some of these sensitive issues?

BARLETTA: I do.

I think he means it. He's going to do something. He's going to secure our borders. He is going to deal with illegal immigration. He is going to make America, our trade deals better, bring jobs back to America. All of these things, I believe him.

He's a successful businessman, and he's not a politician. And by the amount of support that he has in America by Democrats and Republicans and independents, I think he's going to go into the general election with a lot of support.

BLITZER: Congressman Lou Barletta of Pennsylvania, thanks very much for joining us.

BARLETTA: Thank you. Thank you.

BLITZER: We are watching that Trump rally in Montana right now. We are standing by to hear directly from the presumptive Republican presidential nominee. You're looking at live pictures.

Also, a CNN exclusive, how ISIS fighters are infiltrating Europe by hiding among migrants.

Plus, a look inside President Obama's next home. How will Secret Service agents protect the first family in this relatively densely crowded neighborhood?

(COMMERCIAL BREAK)

[18:27:50]

BLITZER: Breaking news tonight, Donald Trump reaching 1,238 delegates, topping the number needed to be the Republican presidential candidate when the party convenes in July.

Now that he has crossed that number for all practical purposes, he has wrapped up, he has clinched the Republican nomination, Dana, does that put a lot more pressure on other Republicans who have waited to go in and endorse him?

DANA BASH, CNN SENIOR CONGRESSIONAL CORRESPONDENT: A little bit, but I feel like that was cooked a couple of weeks ago, the idea that he was going to get to this point, since there was nobody else in the race. I think it's going to be more of an issue and there will be more

pressure as we get to the actual convention, which kind of by definition is the -- and by tradition is the time for Republicans to gather and rally around their person, their man historically.

I think that's really going to be the key time. It's still -- there are a lot of people who are going on board with Trump, a lot more than we thought there would be, given the intense scrutiny and the intense -- I'm not even sure -- I'm trying to think of a diplomatic word to use. I don't even think there is one.

People didn't think he was a real conservative. And they still are not sure about his temperament. But there's a lot more support than there was. It's going to take a little bit more time for...

(CROSSTALK)

BLITZER: Now that he has clinched the nomination, David, do you think we are going to see a significant change in his tone? Because the tone he's had over the past nearly year has gotten him to where he is right now.

DAVID CHALIAN, CNN POLITICAL DIRECTOR: It has. And he knows that the context now changes, and he is moving to a general election audience.

He has talked about that actually throughout the season. But I keep going back and forth on this, Wolf. As you observe him, I see someone who is doing things that he didn't do in the nomination season, in terms of bringing the establishment on board, reaching out, having all these meetings and phone calls with every sort of slice of the conservative movement in a way that somebody who really wants to pivot to a general election nominee would do.

(CROSSTALK)

BLITZER: So, why would he go out and criticize the governor of New Mexico, a popular -- a woman, the head of the Republican Governors Association, a Latina?

CHALIAN: All those things.

And so he can't resist. He still can't resist. When he is criticized, when somebody is reluctant to come on board, he gets back into that mode. As you said, it's what brought him to this dance. And he can't resist...

BASH: And it's who he is.

CHALIAN: ... going there again. And it's who he is.

[18:30:11] And yet you see some moments where he really does want to elevate in some way, and then he just can't resist the opportunity --

BLITZER: Did you notice, David, that he seemed to contradict several of the statements his campaign chairman, Paul Manafort, made in an interview in "Huffington Post" at his news conference today? That was a little awkward, wasn't it?

DAVID SWERDLICK, ASSISTANT EDITOR, THE WASHINGTON POST: Well, he seems to contradict himself on a lot of things, Wolf.

BLITZER: He was contradicting what Paul Manafort said.

SWERDLICK: -- contradict his campaign manager, right. I think that this is a tenuous time for Trump because, like David is saying, he can't resist getting in some of these fights. I do think that Manafort has served him well, but they're in this lull period now where there's going to be more scrutiny on these little side issues rather than the main issue because he doesn't have any competition right now. And I think even though it helps him to have won the nomination and have sewn it up, I do think there's a danger for him in the sense that, his supporters have been animated by all of the sense of aggrieved status, that the Republican Party has pushed them out, right? And now you're in this mode where he's -- it looks more like a coronation, and I think this poses a problem for them.

BASH: Exactly. I think one of the answers to your question about whether he's going to change now was today. No, Elizabeth Warren is not in his party, and it benefits him politically to spar with her, but to call her Pocahontas again and continue to do that -- especially in a place like North Dakota which has a huge Native American population, you had what's kind of a very unusual moment, you had a reporter there who appeared to be Native American saying, that's offensive.

CHALIAN: Right. This wasn't just part of the stump this time. He's actually being questioned about it.

BASH: Exactly. So I think that is an answer to your question, no.

BLITZER: You know, he did have another phone conversation with Speaker of the House, Paul Ryan. Both of them said it was a good conversation, but he's still not there, Paul Ryan, ready to endorse the presumptive Republican nominee. That's unprecedented, for a speaker, for someone of his own party, not to go ahead and endorse.

CHALIAN: Yes, I think Paul Ryan is just very publicly going through the process that many, many Republican office holders and voters that were with other candidates in this nomination season, are going through to get to Trump. I have no doubt that when the convention rolls around in Cleveland in July, Paul Ryan is going to be a Trump supporter. You can see he is laying the ground work and all the pieces to get there. But I think he -- there's something that's clear in his motivation that he is wanting to do this in public fashion. I think if you speak to people around him, yes, it gives him leverage, and it helps him bring the party along. He is part of them piecing together for Trump a unified party.

SWERDLICK: Yes, once he gives away that endorsement, essentially, he's just like every other congressman that's endorsed Trump. He's lost that leverage. I also think, though, that the longer he waits, if something goes wrong with Trump down the road, if Trump loses the general election, he can say, you know, he was hesitant, he wasn't fully on board, whereas if he just goes full on for Trump, he's in the same boat as the rest of the party.

BLITZER: Or you think he's looking at four years in case he decides to run for president? Is that what you're suggesting?

SWERDLICK: I'm not necessarily saying that, but he will presumably be the speaker for the foreseeable future, and if he's going to have sort of a handle, he's going to have the reins on his caucus, he's got to have his own power.

BLITZER: You heard the President, Dana, today, he's at the G7 summit in Japan -- say, world leaders are rattled by Donald Trump. Trump took that as saying, there's nothing wrong with that. I like to rattle people. In business that's good to keep them guessing. What was your analysis of that?

BASH: I think that if he became president one day and he said something to rattle the stock market and the economy in this country and around the world, was rattled based on something he said, he would probably have a different view. Yes, it's good to rattle the cages of Washington and shake things up and I think that's what he was trying to say, that the whole premise of his candidacy is to change things and to get people thinking and to get people nervous about the status quo. That's why people like him. But when you're talking about the world stage, you know this, you've covered the White House, you're an expert on international affairs, it's a little bit different.

CHALIAN: I don't think we should lose sight of what a huge thing that is, that the sitting president of the United States of America on foreign soil has decided to basically nullify publicly one of the nominees to be his successor on the world stage in that way. That is just -- talk about unprecedented stuff, that is just amazing. You can see, clearly President Obama is eager to get on the field and engaged in this campaign, but -- and his legacy is at stake and he knows that. But I just was taken aback by -- just as unconventional as the Donald Trump candidacy is, so was this response from the sitting president of the United States.

SWERDLICK: That's something that the Obama campaign complained about George Bush doing in 2008.

[18:35:01] BLITZER: Yes, I'm old enough to remember that there used to be a saying, politics stops at the water's edge, but clearly in recent years, that has not been true. All right, guys. Stand by. Much more to discuss, including my interview with Hillary Clinton. She's reacting now to that State Department Inspector General report on her e-mail. We will be right back.

(COMMERCIAL BREAK)

[18:40:01] BLITZER: Hillary Clinton calling Donald Trump, and I'm quoting her now, an unqualified loose cannon. In an interview with the Democratic presidential frontrunner last hour, she told me, every American should be concerned because Donald Trump, she says, is within reach of the most important job in the world. CNN's Sunlen Serfaty has the latest on the Democratic race. Sunlen, you're in Ventura, California right now, where Bernie Sanders just held a rally. What's the latest there?

SUNLEN SERFATY, CNN CORRESPONDENT: That's right, Wolf. Both Bernie Sanders and Hillary Clinton are out campaigning here in California tonight where polls in recent days have actually showed that Sanders has been able to close the gap with her significantly, this coupled with the questions over her private e-mail server, certainly not the way Hillary Clinton wanted to wrap this up.

(BEGIN VIDEOTAPE)

HILLARY CLINTON (D), PRESIDENTIAL CANDIDATE: Hello.

SERFATY: Hillary Clinton facing headwinds in her quest to close out the primary.

CLINTON: This election is a make or break election.

SERFATY: A fresh poll out of California shows Bernie Sanders is closing the gap. It is now nearly a dead heat. This comes as Clinton is facing new scrutiny over her use of a private e-mail server as Secretary of State.

CLINTON: This report makes clear that personal e-mail use was the practice under other secretaries of state, and the rules were not clarified until after I had left.

SERFATY: Clinton back on defense after the State Department's Inspector General's scathing report, alleging she violated federal rules.

CLINTON: As I said many times, it was still a mistake, if I could go back I would do it differently, and I understand people have concerns about this, but I hope voters look at the full picture of everything that I've done and the full threat posed by a Donald Trump presidency.

SERFATY: The report did find one former secretary of state, Colin Powell, used private e-mail as well, but not in the same way Clinton did. The report also notes the rules were updated the year Clinton took office and she and her staff refused interviews with the State Department's own investigators. All of this giving new ammunition to Donald Trump.

DONALD TRUMP (R), PRESIDENTIAL CANDIDATE: Actually, I sort of like her in the race. I want to run against her. Look, she has bad judgment. This was all bad judgment. Probably illegal, we'll have to find out what the FBI says about it.

SERFATY: And Trump on the late night, joking, if Hillary Clinton won't debate Bernie Sanders, he will.

JIMMY KIMMEL, TELEVISION HOST: He wants to know if you will debate him?

TRUMP: Yes, I am. How much is he going to pay me?

SERFATY: The question was actually orchestrated by the Sanders campaign, arranged ahead of time with Jimmy Kimmel.

TRUMP: I would love to debate Bernie, actually. I mean, the problem with debating Bernie, he is going to lose.

SERFATY: Meantime, from abroad, President Obama downplaying any Democratic disarray.

BARACK OBAMA, PRESIDENT OF THE UNITED STATES: During primaries, people get a little grumpy with each other. It's just the nature of the process.

SERFATY: Saying there's not much ideological difference between Sanders and Clinton, calling for unity.

OBAMA: I think that it's important for us to try to end this in a way that leaves both sides feeling proud of what they've done.

(END VIDEOTAPE)

SERFATY: And tomorrow, Hillary Clinton will go on the air here in California for the first time this campaign. That's certainly a sign, especially given this latest poll here in California, Wolf, that she knows she has to work for it and takes his challenge here seriously.

BLITZER: When she goes on the air, you mean, with campaign commercials, right?

SERFATY: Campaign commercials, yes.

BLITZER: Sunlen Serfaty reporting for us from Ventura, California. Thanks very much. Let's bring back our panel. So he's crossed the threshold, Dana. It clearly is a significant moment. Hillary Clinton hasn't crossed the threshold yet, but she believes that voters will be more concerned about Donald Trump as president of the United States than her e-mail controversy. Is she right?

BASH: We'll see. That, I think, is going to turn out to be the fundamental question of the election, and not so much specifically about her e-mails but about whether or not his "crooked Hillary" line is going to work or whether her line, her sentiment that he shouldn't be president, he is not ready to be president, he doesn't have the temperament to be president, and that people should judge her on her years of experience, whether that will be the thing that rules the day.

CHALIAN: They clearly know they have this honest and trustworthy deficiency. It's something that they're clearly aware of. They also, right now, have this lingering Democratic nomination race. So they know that they don't have the party fully consolidated the way Donald Trump is doing right now. So that will work to her benefit once that race ends as well in terms of the polling. But look what she did today. She seized on Donald Trump clinching

1,237 to get on the phone with you and do an interview with you so that she can make that comparison and say, OK, we can talk about the e-mail thing I have been talking about for a year, but really?

[18:45:07] That's going to be her argument, is this like -- she's going to make this "loose cannon, he's dangerous, he's divisive" argument, and she will be happy every day to contrast that they think that contrast works for them.

But it is clear honest and trustworthiness will be and her likeability factor will be the thing she has to fix from now to November.

BASH: I have one thing to that, because I've been working on a story about this in the CBS News/"New York Times" poll last week, Hillary Clinton 64 percent of voters said that they do not consider her honest and trustworthy. Donald Trump, 64 percent. The exact the same number said that they don't consider him honest and trustworthy.

The question is, whether it's going to matter to each of their prospective voters who are kind of in the undecided category?

BLITZER: Do you think this Trump/Sanders debate is really going to take place?

SWERDLICK: I'm not sure it's going to take place because what I hear in Trump's comments already is this idea, well, Sanders will lose, what's the point anyway.

But Trump risks a little bit looking like he's afraid to debate Sanders. Sanders is the one person who has nothing to lose. So, he could -- he has challenged Clinton, he's challenged Trump, he's saying I'll take all comers.

The problem for Clinton is that she missed this opportunity, going back to this idea about, you know, the message they want to get out that he's a loose cannon, you say it on a debate stage, it's much more amplified. I'm not sure why she passed on that.

BLITZER: All right, guys. Stand by.

Hillary Clinton was very strong in saying that he's not just a loose cannon but a threat to the United States as well. Let's get some more on that. Stand by for that.

Meanwhile, there's another story we are following, Washington's most famous family is moving across town. President Obama has leased a mansion in one of the Capitol's most exclusive neighborhoods where the first family live after they leave the White House on January 20th next year.

CNN's Brian Todd has more.

Brian, a lot of security concerns surrounding the president's move.

BRIAN TODD, CNN CORRESPONDENT: They sure are, Wolf. Here's the house that everybody is talking about, this beautiful brick Tudor mansion in northwest D.C., 8,200 square feet with a lot of terrific features. But, Wolf, tonight, security experts are telling us some of those features in the house may have to be overhauled.

(BEGIN VIDEOTAPE)

TODD (voice-over): It may be about as close to feeling like you live in the White House as a former president can get. A grand foyer with marble flooring, a gourmet kitchen with hardwood floors and six-burner stove, an expansive fenced in backyard.

This swanky multimillion dollar mansion in one of Washington's most desired neighborhoods may be the post-presidential home of Barack and Michelle Obama. Tonight, neither the first couple or White House will confirm if the Obamas have signed the lease on the nine bedroom, eight and a half bath brick Tudor.

But sources tell CNN they have settled on a home in Washington's upscale Kalorama neighborhood.

The president has said they'll stay in Washington for a couple years after leaving the White House to accommodate his younger daughter.

BARACK OBAMA, PRESIDENT OF THE UNITED STATES: Cause, transferring someone in the middle of high school would really be, tough.

TODD: The house was sold in 2014 for more than $5 million and it's now owned by Joel Lockhart, who was White House press secretary under Bill Clinton. Lockhart wouldn't comment on the reports first made by "Politico" that he is leasing to the Obamas for a rental price of $22,000 a month, but experts say it's the kind of property a president would want.

Woodrow Wilson lived in this neighborhood. Hillary Clinton owns a house nearby. The house also has an au pair suite, which could accommodate Marion Robinson, Michelle Obama's mother. She's lived with the family at the White House.

But there are some features that may have to change in order for the Secret Service to continue to protect Mr. Obama.

ANTHONY CHAPA, FORMER SECRET SERVICE ASSISTANT DIRECTOR: The door should be made bulletproof door, just as if it were an embassy and the glass, the glass presents a problem. One way of addressing it is putting ballistic panes behind the architecture that's here.

TODD: Former Secret Service official Anthony Chapa once protected former vice president Al Gore who live nearby, he says Secret Service officers will be posted outside this house, sometimes even in the wooded area across the street.

Other adjustments?

(on camera): Even these are a big security issue.

CHAPA: It presents a challenge, that's for sure, because what is under it. It says sewer. Where does the sewer flow? And the fact that it's right in front of the door. So, an evaluation will be made, do we need to open these and inspect them, shut down, do we weld them shut, or maybe we work with the city to move this.

TODD (on camera): Even the neighbors will come under the security umbrella.

CHAPA: We would actually need to know who is sleeping in these bedrooms up here.

TODD (on camera): Why? The neighbors? Why?

CHAPA: We want to know what is going on in those, and want to inform them, want to inform us. They're going to be witnesses to those things.

TODD: Tonight, the Secret Service won't comment on whether it's studying how to protect this house or how much it would cost the taxpayers.

(END VIDEOTAPE)

[18:50:05] TODD: Now, other than the obvious luxury, residents say they like this part of the city because it's convenient to other parts of Washington and because it is quiet. One neighbor said the president should be welcome here as long as he doesn't get too rowdy -- Wolf.

BLITZER: Traffic, is that a big issue on the street where you are right now?

TODD: It really is, Wolf. We're going to pivot here, some of the neighbors looking at the house. This is the street where the president's perspective house is.

If you look down here, it's a narrow street. You've got taxis on either side. When we came earlier, there were a lot of cabs lining the side of the street. So parking is a huge issue here. A narrow street. The Islamic center down there, a lot of cabs coming in and out of this street.

One person, the former Secret Service officer we spoke to, Tony Chapa, said they may have to turn this street into a one-way street if the president ends up moving here.

BLITZER: A lot of Muslim taxi drivers parking there so they can walk to the mosque and pray and then get back in their vehicles.

All right. Brian, thanks very much.

Just ahead, more on the breaking political news. Donald Trump closing the deal, locking down the delegates he needs to become the Republican presidential nominee.

Plus, the ominous new ISIS tactic to get terrorists into Europe. It's a CNN exclusive. (COMMERCIAL BREAK)

[18:55:47] BLITZER: There are ominous new developments in the migrant crisis unfolding in Europe. We're now learning that ISIS fighters are hiding among the migrant masses, many of them being smuggled through Libya.

NICK PATON WALSH, CNN SENIOR INTERNATIONAL CORRESPONDENT (voice-over): This is the moment when desperate dreams come to an end. We're with the Libyan immigration police inside a warehouse of migrant hopefuls that just raided right on the trip of the beach front. As Turkey and Greece close their shores, the Libyan route to Europe has exploded again.

Here, among the squalor that a lifetime savings buys is where fantasies of a future in Europe fall apart.

(on camera): Where are you from?

EUGENE, NIGERIAN REFUGEE: Nigeria.

WALSH (voice-over): Eugene fled ISIS local Boko Haram in Nigeria whose bombs killed his father and his brother and he survived the desert trek until here.

EUGENE: Today, bomb blast, tomorrow bomb blast. We are not safe, after the death of my father and my brothers, let me go out, let me travel out. Every time I talk about them, I feel sad.

WALSH: We leave quickly, as this is the smugglers' neighborhood. But there is a new threat here, smugglers and police telling us that ISIS have hidden fighters among other groups of migrants bound for Europe.

(on camera): This trade in human souls is awful enough until you figure perhaps, ISIS are using this passage of human life into Europe to try and infiltrate the continent with sleeper cells.

Police tell us off camera, they caught different other migrants with ISIS links and a top Libyan intelligence officials warns us, the threat is real.

ISMAIL AL-SHUKRI, MISRATA POLICE COMMANDER (through translator): ISIS can be among the illegal immigrants on the boats. They travel with their families, without weapons as normal illegal immigrants. They will wear American dress and have English language papers so they cause no suspicion.

WALSH: It is a huge and unpatrolable coastline, where smugglers ruled. They talked to one, disguised for his safety, who says in the past two months, ferrying ISIS has become part of the trade. UNIDENTIFIED MALE (through translator): About two weeks ago, a boat

left the ISIS stronghold Sirte. Among them were about 40 ISIS. They were heading to Europe, but bad weather turned them back. Ten days later, they tried again. I don't know if they got there. About a month ago, I got a call from a devout guy I knew is ISIS. He wanted a small boat for 25 people and was willing to pay about $40,000. I didn't take the deal.

WALSH (on camera): Do you and other smugglers feel comfortable moving people who you know may be ISIS towards Europe?

UNIDENTIFIED MALE: Smugglers are only interested in smuggling. ISIS, anyone, they don't care. Melon or watermelon, only money matters.

WALSH (voice-over): The Libyan state is torn apart by in fighting. Its coast guard struggling to even find boats.

(on camera): Fighting the migrant trade across, the whole coastline of the Libyan capital Tripoli, just six boats like this. Some of which not in particularly good service. We simply can't imagine how under-resourced things are here, so close to Europe.

(voice-over): These are the desperate scenes as they try to rescue some African migrants, whose dinghy collapsed late last year. Smugglers now prefer these dinghies, vulnerable to the slightest weather change. A trade born of human misery, some fleeing ISIS themselves, only to find ISIS now seek to hijack their deadly journey to spread more suffering.